In an articulating mechanism, such as a finger of a robot, lightweight and non-backlash characteristics have conventionally been required in order to improve the safety and obtain highly accurate control characteristics. Furthermore, in order to realize a high cost performance, it is desired that the structure of the articulating mechanism be simple and various target articular movements be performed in a wide articular movable range. In addition, the articulating mechanism needs to have a structure with no reverse drive performance, depending on the use application of a joint. Although a gear type articulating mechanism or a wire type articulating mechanism has conventionally been used more frequently to transmit a power in an arm, a finger, or other joint of a robot, it is a fact that these types of articulating mechanisms cannot fulfill most of the above-described characteristics at the same time. Especially when an operation of a follower side where a rotation axis of an actuator forms a predetermined angle is realized in the rotation axis, it is difficult to process the gear and to reduce backlash and the weight in the gear type articulating mechanism. The problems in the wire type articulating mechanism, on the other hand, are the increase in the number of parts to be used, such as a tension adjusting mechanism and a wire turning mechanism, as well as the lowering of the control characteristics due to stretching and interference of the wire. Moreover, realizing a more complicated follower joint movement by using these transmission mechanisms further complicates the structures and increases the weight thereof, and as a result non-reverse drive performance cannot be achieved, unless a worm gear or the like is used. For these reasons, smooth transmission of a power to the follower side by using a three-dimensional cam between a driving side and the follower side has been proposed. Patent Documents 1 and 2 described below should be referred to.    Patent Document 1: Japanese Patent Application Publication No. H7-3576 (see claim 1 of the publication)    Patent Document 2: Japanese Patent Application Publication No. 2004-346959 (see the abstract of the publication)
The invention disclosed in Patent Document 1 is provided with, as shown in FIG. 4, a cam main body 104 performing a rotational movement and a follower 105 engaged with the cam main body 104 and performing a swinging movement, wherein: the rotational movement is translated into the swinging movement; the cam main body 104 is provided with a guide surface 111 formed with a closed curve and formed such that an external shape E of this region constitutes an arc line; the follower 105 is engaged with the guide surface 111; and the rotation axis center is nonrotatably connected to a shaft 106 passing through the center of the external shape E.
In the invention disclosed in Patent Document 2 has, as shown in FIG. 5, a cam type power transmission mechanism 201, which transmits a rotation power between first and second rotating shafts 202, 203 arranged so that rotation center lines 202a, 203a thereof cross each other at a predetermined angle, has a cam 204 attached to the first rotating shaft 202 and a cam follower 205 attached to the second rotating shaft 203, wherein in the cam 204, a cut face obtained by cutting a spherical body in a curved face or a flat face is formed as a cam face 204a, and the first rotation center line 202a is connected to the first rotating shaft 202 so as to pass the center of the spherical body, and the cam follower 205 has a roller 205e attached to the second rotating shaft 203 so as to draw a circular track with a predetermined radius around the rotation center line 203a of the second rotating shaft 203. When one rotating shaft is rotated, the roller 205e of the cam follower 205 relatively slides along the cam face 204a of the cam 204 to finitely rotate the other rotating shafts.
In the invention of Patent Document 1 shown in FIG. 4 among these prior arts, because the external shape E of the surface region of the cam main body 104 constitutes an arc line and the shaft 106 of the follower 105 passes through the center of the external shape E, a follower joint can perform only a rotational movement (reciprocal movement) around an axis line 103 twisted at a right angle to the axial line 102 of the cam main body 104. Moreover, although the rotation of the cam main body 104 can be translated smoothly into the swinging movement of the follower 105 by means of the three-dimensional cam, transmission of the power from the shaft 106 of the follower 105 to a synchronous pulley 109 needs to be performed through a sector gear 108 and a pinion 110, unlike a structure configured only by the follower 105, and therefore the occurrence of backlash in a gear meshing part cannot be prevented, still lowering the conversion accuracy. Further, in these conventional examples, although it is possible to reversely transmit the power from the follower 105, smooth operations cannot be expected.
In the invention of Patent Document 2 shown in FIG. 5, the cam surface 204a of the three-dimensional cam 204 that determines the operation on the follower side having the cam follower 205 is generated by cutting the spherical body in the curved face or the flat face, and, unlike the gear type or wire type articulating mechanism, it is not necessary to increase backlash or provide a tension adjusting mechanism and a wire turning mechanism. Also, reduction in the number of parts and lowering of the control characteristics due to stretching and interference of the wire no longer occur. However, because the cam surface 204a is generated by cutting the spherical body in the curved face or the flat face, the behavior on the cam follower 205 side, i.e., the follower side, is limited, and guiding is performed by the cam surface 204a and the roller 205e of the cam follower 205 at only one point, whereby the transmission of the power by the cam mechanism tends to become unstable.